Steel Sub-Frame

A sub-frame is a steel frame set into the wall opening during the structural stage, before the joinery arrives. Plaster, screed and finishes are completed against the sub-frame; the actual door or window is fitted last, into a clean opening of known size.

What it does

• Fixes the opening to a net size and plumb, so the same joinery size can be used on every floor.
• Protects joinery from plastering and screeding work.
• Spreads the load of heavy doors, fire doors and wide sliding systems into the wall.
• Lets joinery be positioned in the insulation plane on insulated facades.

With and without a sub-frame

Installation

The frame is prepared from box sections as a welded frame to the opening size, fixed to the wall with straps or anchors, and its diagonals are checked. It is supplied primer-coated or galvanised. The table below lists commonly used sections; heavier doors take larger sections.